Methods of Determination of Pathogenic 3Iicrohes. 127 



various media, and the establishment of a suitable 

 temperature. 



Methods of isolation. 



The isolation of mixed germs may be obtained in 

 several different ways. One method of isolation is 

 based upon the different properties of the species to 

 be isolated. Thus, the germs of the septicsemias of 

 the rabbit and of the mouse have been withdrawn 

 from the mass of microbes which pullulate in blood 

 in way of putrefaction, by taking advantage of the 

 fact that these germs are pathogenic for such 

 animals. 



Pasteur has isolated the bacillus anthracis from 

 the septic vibrio in charbonous blood in a state of 

 putrefaction by taking into account the fact that the 

 former is aerobic and the latter anaerobic : cultures 

 in the air give the bacillus anthracis only; those pro- 

 tected from oxygen give the septic vibrio. 



The influence of various chemical agents and that 

 of heat at different degrees are also effectual means 

 of isolation ; they kill some germs or considerably in- 

 terfere with their multiplication, and thus favor the 

 predominance of other less sensitive germs. 



Klebs has succeeded in isolating germs by basing 

 himself upon their unequal distribution in the liquids 

 in which they pullulate. Some, immobile, are found 

 at the bottom or on the walls of the vessels ; others, 

 motile, are uniformly distributed; some again are 

 very greedy of oxygen and are found in the super- 

 ficial layer, ^y withdrawing germs from these vari- 

 ous parts more of one species than of another will 

 be removed, and by repeating the operation several 



